I can see where you're coming from on this. But part of Xavier's psychology comes from his privilege and the social circles he moves in. He insists that Mutants can coexist with Humans, but only if Mutants become 'respectable' by controlling their powers and concealing their physycal oddities. That is, as far as I can tell, purely white privileged thinking. Xavier has never been on the receiving end of prejudice because he looks normal and because his powers enable him to control others without their knowing. That is key to much of the conflict in the X-Men -Xavier has no real empathy with either his students or opponents because he has never experienced what they have. A Black Xavier will ipso facto have been a victim, to at least some extent, of racism, and would have different ideas.

Magneto, who has been right at the bottom, in a concentration camp, both a Jew and a Mutant, breaks with Xavier because he believes that the only way to keep Mutants safe is to make Humans too scared to act against them.

Characters such as Nightcrawler and Beast are allied to Xaviers' cause of coexistence but challenge the strategy of blending in as a denial of identity.

Wolverine, the grizzled veteran, knows only too well that Humans will only accept Mutants when they have a use for them.

You could change the skin-colour of any other character -a Black Kitty Pryde could bring one perspective. Making the Summers brothers Black would bring another.

But Xavier, Magneto and Wolverine should stay white, for the reasons stated above.